The present invention relates generally to optoelectronic devices and more particularly relates to low thermal impedance distributed Bragg reflectors (DBRs) for optoelectronic devices.
The performance of semiconductor lasers, including VCSELs, are limited by many things, such as, for example, lossy waveguides and mirrors, current leakage, non-radiative recombination, photon density, etc. A well-designed VCSEL, however, is limited primarily by heat dissipation. Heat generation within the active area of a VCSEL reduces the gain, differential gain and internal quantum efficiency to the point where the threshold, output power or speed may degrade significantly with increasing temperature. Heat is typically generated within the active area through electrical power dissipation, P=IV, where I and V are the operating current and voltage, respectively. The temperature rise above ambient is then the product of the dissipated power and the thermal impedance of the device, xcex94T=PZtherm.
In an exemplary embodiment of the present invention the thermal impedance of a VCSEL is reduced to provide improved heat dissipation and temperature performance. In one aspect of the present invention the overall thermal impedance of an optoelectronic device may be improved by reducing the thermal impedance of one or both of the mirrors of the device. In one aspect of the present invention, a low thermal impedance optoelectronic device includes an active region adjacent a mirror structure having half-wavelength periods formed from alternating layers having asymmetric optical layer thicknesses. In this embodiment, the thermal impedance of the optoelectronic device may be reduced by increasing the thickness of a high thermal conductivity layer relative to a low thermal conductivity layer within the half-wavelength mirror period.
In another aspect of the present invention, a low thermal impedance optoelectronic device includes an active region adjacent a mirror structure having mirror periods where the thickness of a high conductivity layer within a plurality of the mirror periods is increased in a non-uniform fashion. In this embodiment the mirror period having the thickest high thermal conductivity layer occurs closest to the active region. As an example, starting from the active region the high thermal conductivity layers may have thicknesses of {fraction (7/4)}xcex, 5/4xcex, and xc2xexcex, respectively.
In a further aspect of the present invention, a low thermal impedance optoelectronic device includes an active region adjacent a mirror structure having mirror periods where the thickness of the high thermal conductivity layers is uniformly increased throughout the mirror structure. In this embodiment, the thickness of the high thermal conductivity layers may be increased by an integer multiple of one-half of The transmission wavelength of the optoelectronic device.
In a further aspect of the present invention, a low thermal impedance optoelectronic device includes an active region formed adjacent a DBR having a plurality of mirror periods. In this embodiment the mirror periods include a first layer, formed from a first material having a first thermal conductivity and a second layer, formed from a second material having a second thermal conductivity that is greater than the first thermal conductivity. In this embodiment the thickness of at least a portion of the mirror periods is greater than one-half the wavelength of the light emitted by the optoelectronic device to separate the phonon scattering interfaces and improve the thermal impedance of the device.